ksmbd: remove the leftover of smb2.0 dialect support

Although ksmbd doesn't send SMB2.0 support in supported dialect list of smb
negotiate response, There is the leftover of smb2.0 dialect.
This patch remove it not to support SMB2.0 in ksmbd.

Cc: Tom Talpey <tom@talpey.com>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Ralph Böhme <slow@samba.org>
Cc: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>